1. Field of the Invention
The present invention relates to magnetic sensing elements mainly used for magnetic sensors, hard disk drives, etc., and more particularly, to a magnetic sensing element having an improved magnetic sensitivity and a method for making the same.
2. Description of the Related Art
FIG. 32 is a sectional view of a conventional magnetic sensing element, viewed from a surface facing a recording medium.
The magnetic sensing element shown in FIG. 32 is a spin-valve magnetic sensing element which is one type of giant magnetoresistive (GMR) element using a giant magnetoresistance effect and which detects a recorded magnetic field from a magnetic recording medium, such as a hard disk.
The spin-valve magnetic sensing element includes a multilayer film 8 including a substrate 1, an underlayer 2, a first antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, a free magnetic layer 6, and a protective layer 7 deposited in that order from the bottom; a pair of ferromagnetic layers 9 formed on both sides of the multilayer film 8; a pair of second antiferromagnetic layers 10 formed on the pair of ferromagnetic layers 9; and a pair of electrode layers L formed on the pair of second antiferromagnetic layers 10.
In general, Ptxe2x80x94Mn alloy films are used for the first antiferromagnetic layer 3 and the second antiferromagnetic layers 10; Nixe2x80x94Fe alloy films are used for the pinned magnetic layer 4, the free magnetic layer 6, and the ferromagnetic layers 9; a Cu film is used for the nonmagnetic material layer 5; Ta films are used for the underlayer 2 and the protective layer 7; and Cr films are used for the electrode layers L.
The magnetization of the pinned magnetic layer 4 is aligned in a single domain state in the Y direction (the direction of a fringing magnetic field from the recording medium, i.e., in the height direction) by an exchange anisotropic magnetic field with the first antiferromagnetic layer 3.
Each of the ferromagnetic layers 9 is aligned in a single domain state in the X direction by an exchange anisotropic magnetic field with the second antiferromagnetic layer 10. The free magnetic layer 6 and the ferromagnetic layers 9 are in contact with each other at joints J, thus forming a continuous ferromagnetic body. The free magnetic layer 6 is aligned in a single domain state in the X direction by a so-called xe2x80x9cexchange bias systemxe2x80x9d. In the exchange bias system, surface magnetic charges do not occur at both end faces (joints J) of the free magnetic layer 6, and the magnitude of a demagnetizing field generated in the free magnetic layer 6 can be decreased.
In the magnetic sensing element, a sensing current is supplied from one of the electrode layers L through the second antiferromagnetic layer 10 and the ferromagnetic layer 9 to the free magnetic layer 6, the nonmagnetic layer 5, and the pinned magnetic layer 4. A recording medium, such as a hard disk, travels in the Z direction, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer 6 is changed from the X direction to the Y direction. Electrical resistance changes due to the relationship between the varying magnetization direction of the free magnetic layer 6 and the pinned magnetization direction of the pinned magnetic layer 4 exemplify the magnetoresistance effect. This effect can be detected by a voltage change resulting from electrical resistance changes in the fringing magnetic field from the magnetic recording medium.
In order to fabricate the magnetic sensing element shown in FIG. 32, the underlayer 2, the first antiferromagnetic layer 3, the pinned magnetic layer 4, the nonmagnetic layer 5, the free magnetic layer 6, and the protective layer 7 are deposited on the substrate 1, each being a thin film with a uniform thickness, and then portions other than a portion for forming the multilayer film 8 shown in FIG. 32 are removed by ion milling. Next, the ferromagnetic layers 9 are formed so as to come into contact with side faces 8a of the multilayer film 8, and the second antiferromagnetic layers 10 and the electrode layers L are further deposited on the ferromagnetic layers 9.
That is, in the magnetic sensing element shown in FIG. 32, the side faces 8a of the multilayer film 8 are interfaces trimmed by milling. Even if the ferromagnetic layers 9 are deposited on such interfaces trimmed by milling so as to be in contact with the interfaces, it is difficult to form a continuous ferromagnetic body in which the free magnetic layer 6 and the ferromagnetic layers 9 are joined to each other at the joints J, and therefore it is difficult to align the free magnetic layer 6 stably in a single domain state in the X direction.
Since the joints J between the free magnetic layer 6 and the ferromagnetic layers 9 are on the side faces 8a of the multilayer film 8, it is difficult to magnetically couple the free magnetic layer 6 and the ferromagnetic layers 9 to each other. For this reason, it is also difficult to align the free magnetic layer 6 stably in a single domain state in the X direction.
Additionally, if an angle xcex81 of inclination of the side face 8a of the multilayer film 8 is decreased in order to stabilize the magnetic coupling between the free magnetic layer 6 and the ferromagnetic layers 9, it becomes difficult to form the width of the free magnetic layer 6 in the track width direction (X direction) in a predetermined range.
Moreover, in order to join the free magnetic layer 6 and the ferromagnetic layers 9 reliably in the structure shown in FIG. 32, the thickness of the ferromagnetic layer 9 must be increased. However, if the thickness of the ferromagnetic layer 9 is increased, the unidirectional anisotropic magnetic field of the ferromagnetic layer 9 is decreased, resulting in a difficulty in applying a stable longitudinal bias to the free magnetic layer 6. If the thickness of the ferromagnetic layer 9 is increased, insensitive regions occur at both ends of the free magnetic layer 6, and therefore, satisfactory read sensitivity cannot be obtained in an element with a narrow track width at 0.2 xcexcm or less.
As described above, in the conventional magnetic sensing element shown in FIG. 32 using the exchange bias system, it is difficult to align the free magnetic layer 6 stably in a single domain state by applying a stable longitudinal bias to the free magnetic layer 6.
It is an object of the present invention to provide a magnetic sensing element using the exchange bias system and a method for fabricating the same, in which the free magnetic layer can be aligned stably in a single domain state in the X direction, and magnetic sensitivity can be improved.
In accordance with the present invention, a magnetic sensing element includes a multilayer film including a first antiferromagnetic layer; a pinned magnetic layer, the magnetization direction of the pinned magnetic layer being pinned by the first antiferromagnetic layer; a nonmagnetic material layer; a free magnetic layer, the magnetization direction of the free magnetic layer varying in response to an external magnetic field; a nonmagnetic layer; a pair of ferromagnetic layers; a pair of second antiferromagnetic layers; a first electrode layer; a second electrode layer; and a track width region comprising a central region and pair of sides, wherein the multilayer film has a characteristic track width direction. In the magnetic sensing element, the nonmagnetic layer has a uniform thickness, or the thickness in the central region of the nonmagnetic layer is larger than in its side regions; the pair of ferromagnetic layers are provided on the upper surface of the nonmagnetic layer, the pair of ferromagnetic layers at a predetermined distance apart from one another in the track width direction; the pair of the second antiferromagnetic layers are provided on the pair of ferromagnetic layers; and the magnetization direction of the free magnetic layer is substantially perpendicular to the magnetization direction of the pinned magnetic layer by magnetic coupling with the ferromagnetic layers, the magnetization direction of the ferromagnetic layers being aligned by magnetic coupling with the second antiferromagnetic layers. In the present invention, the magnetization direction of the ferromagnetic layers located under the pair of second antiferromagnetic layers is aligned in the track width direction by magnetic coupling with the second antiferromagnetic layers. The magnetization direction of the side regions of the free magnetic layer formed under the ferromagnetic layers with the nonmagnetic layer therebetween is aligned in a direction antiparallel to the magnetization direction of the ferromagnetic layers by RKKY interactions with the ferromagnetic layers. That is, under the pair of second antiferromagnetic layers, the ferromagnetic layer, the nonmagnetic layer, and the free magnetic layer form a synthetic ferrimagnetic structure such that the magnetization direction of the side regions of the free magnetic layer overlapping with the second antiferromagnetic layers and the ferromagnetic layers is pinned in the direction antiparallel to the track width direction.
On the other hand, the magnetization direction of a track width region of the free magnetic layer, which is the region not overlapping with the second antiferromagnetic layers and the ferromagnetic layers, is directed antiparallel to the track width direction following the side regions in the absence of an applied external magnetic field. When an external magnetic field is applied in a direction (height direction) perpendicular to the track width direction, the magnetization direction of the track width region of the free magnetic layer is changed to the height direction.
Electrical resistance changes due to the relationship between the varying magnetization direction of the free magnetic layer in the track width region and the pinned magnetization direction of the pinned magnetic layer exemplify the magnetoresistance effect. This effect is detectable by a voltage change resulting from electrical resistance changes in external magnetic fields, such as fringing magnetic fields from a magnetic recording medium.
In accordance with the present invention, since the synthetic ferrimagnetic structure is formed by the ferromagnetic layer, the nonmagnetic layer, and the free magnetic layer under the second antiferromagnetic layers, it is possible to increase a unidirectional anisotropic magnetic field for aligning the magnetization direction of the free magnetic layer in the side regions in a predetermined direction.
Consequently, it is possible to prevent the magnetic track width from being increased because of a change in the magnetization direction of the free magnetic layer in the side regions.
Even if the exchange coupling magnetic field between the second antiferromagnetic layers and the ferromagnetic layers is relatively weak, the magnetization direction of the free magnetic layer can be easily and reliably directed in substantially perpendicular to the magnetization direction of the pinned magnetic layer. Therefore, even in the region in which the thickness of the second antiferromagnetic layers is decreased, a sufficient unidirectional anisotropic magnetic field can be obtained.
A track width (optical track width) region of the magnetic sensing element defined by a predetermined distance in the track width direction between the pair of ferromagnetic layers effectively contributes to regeneration of the recorded magnetic field, constituting a sensitive region exhibiting the magnetoresistance effect.
That is, in the magnetic sensing element of the present invention, since the optical track width corresponds to the magnetic track width and insensitive regions do not occur, it is possible to prevent the read output from decreasing when the optical track width of the magnetic sensing element is reduced to satisfy demands for increasing recording density.
Since the magnitude of the bias magnetic field applied to the free magnetic layer becomes equal to the magnitude of the magnetic moment per unit area of the free magnetic layer, wherein the magnetic moment is defined by the product of the saturation magnetization (Ms) and the film thickness (t), a high output magnetic sensing element having a high sensitivity is produced.
In accordance with the present invention, since the free magnetic layer is composed of a magnetic material that extends to the regions below the second antiferromagnetic layers and the ferromagnetic layers, it is possible to reduce the influence of the demagnetizing field generated by surface magnetic charges at both end faces of the free magnetic layer.
Moreover, in the present invention, since the interface between the free magnetic layer and the nonmagnetic layer and the interfaces between the nonmagnetic layer and the ferromagnetic layers are not required to be trimmed by milling, it is possible to prevent decreases in the unidirectional anisotropic magnetic fields which align the magnetization directions of the side regions of the free magnetic layer in a predetermined direction.
Further, since the free magnetic layer and the ferromagnetic layers are magnetically coupled to each other with the nonmagnetic layer therebetween by the RKKY interactions, even when the interface between the free magnetic layer and the nonmagnetic layer or the interfaces between the nonmagnetic later and the ferromagnetic layers are surfaces trimmed by milling, it is possible to obtain unidirectional anisotropic magnetic fields which have a magnitude sufficient for aligning the magnetization directions of the side regions of the free magnetic layer in a predetermined direction.
In the present invention, since the ferromagnetic layers and the second antiferromagnetic layers are deposited on the planar nonmagnetic layer, the deposition step for the ferromagnetic layers and the second antiferromagnetic layers is easily controlled. In particular, in the synthetic ferrimagnetic structure including the ferromagnetic layer, the nonmagnetic layer, and the free magnetic layer, the thickness of the ferromagnetic layer can be reduced, thereby allowing an increase in the spin-flop magnetic field between the ferromagnetic layer and the free magnetic layer.
In the present invention, preferably after the track width region of the nonmagnetic layer is covered by a resist layer, the ferromagnetic layer and the second antiferromagnetic layers are formed by sputtering a ferromagnetic material and an antiferromagnetic material on the regions of the nonmagnetic layer not covered by the resist layer. This allows for the upper surfaces of the ferromagnetic layers and the second antiferromagnetic layers to form inclined surfaces or curved surfaces relative to the upper surface of the nonmagnetic layer.
As described above, by sputtering the ferromagnetic material and the antiferromagnetic material on the nonmagnetic layer, it is possible to produce a magnetic sensing element of this invention in which the ferromagnetic layers and the second antiferromagnetic layers are provided on the nonmagnetic layer having a planar upper surface.
Preferably, the nonmagnetic layer is composed of a conductive material. Consequently, the nonmagnetic layer exhibits a spin filter effect which can improve the magnetic sensitivity of the magnetic sensing element.
More preferably, the nonmagnetic layer is composed of any one of Ru, Rh, Ir, Os, and Re, or an alloy of at least two of these elements.
More preferably, the nonmagnetic layer is composed of Ru and has a thickness of 0.8 to 1.1 nm. Consequently, RKKY interactions between the ferromagnetic layers and the side regions of the free magnetic layer can be increased.
Preferably, the magnetic sensing element further includes a conductive material layer placed between the nonmagnetic layer and the free magnetic layer, the conductive material layer having a lower resistivity than that of the nonmagnetic layer. Consequently, a higher spin filter effect can be exhibited than in the case in which only a nonmagnetic layer is used, thereby further improving the magnetic sensitivity of the magnetic sensing element.
When the conductive material layer is formed, preferably, the nonmagnetic layer is composed of Ru and has a thickness of 0.4 to 1.1 nm. Preferably, the conductive material layer is composed of Cu and has a thickness of 0.3 to 0.5 nm.
If the nonmagnetic layer deposited in contact with the upper surface of the free magnetic layer is composed of a conductive material or if the conductive material layer is formed between the nonmagnetic layer and the free magnetic layer, the nonmagnetic layer can act as a back layer exhibiting a spin filter effect.
When a sensing current is applied to a spin-valve magnetic sensing element, conduction electrons mainly move in the vicinity of the nonmagnetic material layer having a small electrical resistance. The probability is that two types of conduction electrons, i.e., spin-up conduction electrons and spin-down conduction electrons, will be present in equal quantity.
The rate of change in magnetoresistance of the spin-valve magnetic sensing element is positively correlated with a difference in the mean free path between the two types of conduction electrons.
The spin-down conduction electrons are always scattered at the interface between the nonmagnetic material layer and the free magnetic layer, regardless of the direction of an applied external magnetic field. The probability of transferring electrons to the free magnetic layer remains low. Thus, the mean free path of the spin-down conduction electrons remains shorter than that of the spin-up electrons.
In contrast, the spin-up conduction electrons have an increased probability of transferring electrons from the nonmagnetic material layer to the free magnetic layer when the magnetization direction of the free magnetic layer is set parallel to the magnetization direction of the pinned magnetic layer by an external magnetic field. Consequently, the mean free path is increased. As the magnetization direction of the free magnetic layer is varied from a state parallel to the magnetization direction of the pinned magnetic layer due to an external magnetic field, the probability of being scattered at the interface between the nonmagnetic material layer and the free magnetic layer is increased and the mean free path of the spin-up conduction electrons is decreased.
As described above, the mean free path of the spin-up conduction electrons greatly changes in comparison with the mean free path of the spin-down conduction electrons, thereby greatly changing the difference between the two mean free paths. As a result, the mean free path of the entire conduction electrons greatly changes so as to increase the rate of change in magnetoresistance (xcex94R/R) of the spin-valve magnetic sensing element.
If a back layer is joined to the free magnetic layer, spin-up electrons passing through the free magnetic layer can also move into the back layer. Thus, the mean free path of the spin-up electrons can be further extended. Moreover, since the so-called xe2x80x9cspin filter effectxe2x80x9d can be exerted, the difference in the mean free path of conduction electrons can be increased, resulting in a further improvement in the rate of change in magnetoresistance of the spin-valve magnetic sensing element.
In the present invention, preferably, the free magnetic layer has a thickness of 1.5 to 4.5 nm.
The difference in the mean free path between the spin-up conduction electrons and the spin-down conduction electrons due to the spin filter effect is more effectively increased when the thickness of the free magnetic layer is relatively small.
If the thickness of the free magnetic layer is less than 1.5 nm, it is difficult for the free magnetic layer to function as a ferromagnetic material layer so as to obtain a sufficient magnetoresistance effect. In addition, since conduction electrons which are subjected to diffusive scattering without being subjected to specular reflection are present, the rate of change in resistance is reduced.
If the thickness of the free magnetic layer is more than 4.5 nm, there, is an increased number of spin-up conduction electrons scattering before reaching the back layer. This reduces the increase in the rate of change in resistance due to the spin filter effect.
The magnetic sensing element of the present invention may be a magnetic sensing element of a current-in-plane (CIP) type, wherein the electrode layers are provided on the side regions in the track width direction of the multilayer film so that a current flows parallel to the planes of the individual layers of the multilayer film.
Preferably, the electrode layers are provided on the pair of second antiferromagnetic layers and the edges of the electrode layers at the track width region sides overlap with the edges of the second antiferromagnetic layers at the track width region sides.
Alternatively, the electrode layers are provided on the pair of second antiferromagnetic layers and the edges of the electrode layers at the track width region sides are placed closer to the side faces of the multilayer film compared to the edges of the second antiferromagnetic layers at the track width region sides.
An upper shielding layer and a lower shielding layer, each composed of a magnetic material, may be formed on the upper surface and the lower surface of the magnetic sensing element of the present invention with insulating upper and lower gap layers therebetween.
If the edges of the electrode layers at the track width region sides are placed closer to the side faces of the multilayer film compared to the edges of the pair of second antiferromagnetic layers at the track width region sides, steps between the upper surface of the nonmagnetic layer in the track width region and the upper surfaces of the electrode layers and the second antiferromagnetic layers can be gentler. Therefore, even if the thickness of the upper gap layer is decreased, the upper gap layer can be formed reliably on the steps. Moreover, because there is more reliable protection against electrical short-circuiting between the upper shielding layer and the electrode layers, second antiferromagnetic layers, and ferromagnetic layers, the magnetic sensing element can be rendered suitable for gap narrowing.
If the distance between the upper shielding layer and the lower shielding layer is increased in the vicinity of both sides of the track width region of the multilayer film, magnetic fields originating from the recorded tracks of a recording medium at both sides of the recorded track easily enter the magnetic sensing element, thereby increasing the effective track width and facilitating crosstalk between recorded tracks.
In the present invention, as described above, since the steps between the upper surface of the nonmagnetic layer in the track width region and the upper surfaces of the electrode layers and the second antiferromagnetic layers can be gentler, it is possible to decrease the effective track width by preventing an increase in the distance between the upper shielding layer and the lower shielding layer in the vicinity of both sides of the track width region of the multilayer film.
Alternatively, the electrode layers are preferably provided on the second antiferromagnetic layers and the edges of the electrode layers at the track width region sides extend from the edges of the second antiferromagnetic layers at the track width region sides toward the central region of the multilayer film.
The ferromagnetic layers and the second antiferromagnetic layers are composed of materials having a larger resistivity than that of the electrode layer. If the electrode layer is disposed only on the ferromagnetic layers and the second antiferromagnetic layers, a DC current supplied to the electrode layer flows through the nonmagnetic layer, the free magnetic layer, the nonmagnetic material layer, and the pinned magnetic layer via the ferromagnetic layer and the second antiferromagnetic layer, thereby increasing the DC resistance of the magnetic sensing element.
When the edges of the electrode layers at the track width region sides extend from the edges of the second antiferromagnetic layers at the track width region sides toward the central region of the multilayer film, since the edges of the electrode layers at the track width region sides extend over the nonmagnetic layer, a DC current supplied to the electrode layer can be transmitted without passing through the ferromagnetic layer and the second antiferromagnetic layer. Accordingly, the DC resistance of the magnetic sensing elements of the present invention can be reduced.
The magnetic sensing element of the present invention may be a magnetic sensing element of a current-perpendicular-to-plane (CPP) type, in which the electrode layers are provided on the upper and lower surfaces of the multilayer film so that a current flows perpendicular to the planes of the individual layers of the multilayer film.
In the CPP-type magnetic sensing element of the present invention, the upper electrode layer over the multilayer film may be composed of a magnetic material and may further act as an upper shielding layer.
Preferably, an insulating layer is provided on the second antiferromagnetic layers and an upper electrode layer is formed over the insulating layer and the nonmagnetic layer. Consequently, it is possible to reduce the amount of shunt in the sensing current from the upper electrode layer to the second antiferromagnetic layers. Thus the output of the magnetic sensing element is improved and narrowing of the effective track width is accelerated.
The lower electrode layer under the multilayer film may be composed of a magnetic material and may also act as a lower shielding layer.
Preferably, a protruding section extending toward the multilayer film is provided in the center of the lower electrode layer in the track width direction such that the upper surface is in contact with the lower surface of the multilayer film and insulating layers are provided between the multilayer film and the lower electrode layer on both sides of the protruding section between the lower surface of the multilayer film and upper surface of the side regions of the second electrode layer in the track width direction of the lower electrode layer. In such a structure, the width of the sensing current path is reduced such that the effective track width can be further narrowed.
Preferably, the upper surface of the protruding section is flush with the upper surfaces of the insulating layers provided on the side regions of the lower electrode layer. Consequently, the multilayer film to be formed on the lower electrode layer and the insulating layers can be stably formed on the planar surface so as to better stabilize the magnetic sensing element.
Preferably, the nonmagnetic material layer is composed of a nonmagnetic conductive material. The magnetic sensing element in which the nonmagnetic material layer is composed of a nonmagnetic conductive material is referred to as a spin-valve GMR-type magnetoresistive element (CPP-GMR).
In the CPP-type magnetic sensing element of the present invention, the nonmagnetic material layer may be composed of an insulating material. Such a magnetic sensing element is referred to as a spin-valve tunneling magnetoresistive element (CPP-TMR).
Additionally, the free magnetic layer and the ferromagnetic layer must have different magnetic moments per unit area. The magnitude of the magnetic moment of the free magnetic layer or the ferromagnetic layer per unit area is the product of the saturation magnetization (Ms) and the thickness (t) of the layer.
Preferably, the pinned magnetic layer includes a plurality of ferromagnetic sublayers laminated to each other, a nonmagnetic intermediate sublayer being placed between the two adjacent ferromagnetic sublayers, and the magnetization directions of the two adjacent ferromagnetic sublayers are in an antiparallel, ferrimagnetic state.
When the pinned magnetic layer has such a structure, the plurality of ferromagnetic sublayers pin each other""s magnetization directions. As a result, it is possible to pin the magnetization direction of the entire pinned magnetic layer strongly in a predetermined direction and increase the exchange coupling magnetic field (Hex) between the second antiferromagnetic layer and the pinned magnetic layer.
Additionally, the demagnetizing field (dipole magnetic field) due to the pinned magnetization of the pined magnetic layer can be cancelled because the magnetostatic coupling magnetic fields of the plurality of ferromagnetic sublayers counteract each other. As a result, the contribution of the demagnetizing field (dipole magnetic field) by the pinned magnetization of the pinned magnetic layer to the variable magnetization of the free magnetic layer can be reduced.
Consequently, the variable magnetization of the free magnetic layer is more easily adjusted in a desired direction, and it is possible to obtain a magnetic sensing element which exhibits superior symmetry and low asymmetry.
Herein, asymmetry is defined as the degree of asymmetry of a regenerated output waveform. If the waveform is symmetrical, the asymmetry is decreased. Therefore, as the asymmetry is brought closer to zero, the regenerated output waveform has a more superior symmetry.
The asymmetry is zero when the direction of the variable magnetization of the free magnetic layer and the direction of the pinned magnetization of the pinned magnetic layer are perpendicular to each other. When the asymmetry is greatly increased, it is not possible to read the data accurately from the media, resulting in an error. Therefore, as the asymmetry is brought closer to zero, the reliability of processing regenerated signals is improved, resulting in a superior spin-valve magnetic sensing element.
In general, the demagnetizing field (dipole magnetic field) Hd has a nonuniform distribution in which the values are large at the ends and small in the center in the element height direction. Therefore, in some cases, the free magnetic layer may be prevented from being aligned in a single-domain state. However, by using the pinned magnetic layer having the laminated structure as described above, the dipole magnetic field Hd can be substantially set at zero. Thus, nonuniform distribution of the magnetization is prevented from occurring due to the formation of domain walls in the free magnetic layer. This makes it possible to prevent Barkhausen noise, etc. from occurring.
In the present invention, the free magnetic layer preferably includes a plurality of ferromagnetic sublayers laminated to each other, a nonmagnetic intermediate sublayer being placed between two adjacent ferromagnetic sublayers. The magnetization directions of the two adjacent ferromagnetic sublayers are in an antiparallel, ferrimagnetic state. Consequently, the same advantage is obtained as in the case in which magnetic sensitivity is improved by decreasing the thickness of the free magnetic layer.
Additionally, the magnitude of the magnetic moment per unit area of the ferromagnetic sublayer is represented by the product of the saturation magnetization (Ms) and the thickness (t) of the ferromagnetic sublayer.
The nonmagnetic intermediate sublayer may be composed of any one of Ru, Rh, Ir, Os, Cr, Re, and Cu, or an alloy of at least two of these elements.
In the present invention, at least one of the ferromagnetic layer or the free magnetic layer is preferably composed of a magnetic material represented by the formula CoFeNi, wherein the Fe content is in the range of 9 to 17 atomic percent, the Ni content is in the range of 0.5 to 10 atomic percent, and the balance is Co.
Preferably, the magnetic sensing element of the present invention further includes an interlayer composed of Co or a CoFe alloy between the free magnetic layer and the nonmagnetic material layer.
When the interlayer is formed, at least one of the ferromagnetic layer or the free magnetic layer is preferably composed of a magnetic material represented by the formula CoFeNi, wherein the Fe content is in the range of 7 to 15 atomic percent, the Ni content is in the range of 5 to 15 atomic percent, and the balance is Co.
Preferably, both the ferromagnetic layer and the free magnetic layer are composed of magnetic material represented by the formula CoFeNi.
In the present invention, the ferromagnetic layer, the nonmagnetic layer, and the free magnetic layer form a laminated ferrimagnetic structure under the second antiferromagnetic layer in which the magnetization directions of the ferromagnetic layer and the free magnetic layer sandwiching the nonmagnetic layer are in an antiparallel, ferrimagnetic state.
In order to maintain the antiparallel magnetization state appropriately, the exchange coupling magnetic field due to the RKKY interaction between the ferromagnetic layer and the free magnetic layer must be increased by improving the materials for the ferromagnetic layer and the free magnetic layer.
NiFe alloys are often used as magnetic materials for forming the ferromagnetic layer and the free magnetic layer. Although the NiFe alloys have been used for free magnetic layers, etc. due to superior soft magnetic properties, when the laminated ferrimagnetic structure is constructed using the NiFe alloys for the ferromagnetic layer and the free magnetic layer, antiparallel coupling between these layers is not substantially large.
Therefore, in the present invention, a CoFeNi alloy is used for at least one of the ferromagnetic layer and the free magnetic layer, and preferably for both of these layers. By utilizing the improved C-containing alloys of the present invention, antiparallel coupling between the ferromagnetic layer and the free magnetic layer is increased and the magnetizations of the side regions of the free magnetic layer located at both sides in the track width direction are not influenced by an external magnetic field. Thus, side reading can be appropriately suppressed.
FIG. 17 is a conceptual diagram of a hysteresis loop for a so-called xe2x80x9claminated ferrimagnetic structurexe2x80x9d in which thin films composed of ferromagnetic materials are laminated with a nonmagnetic material layer therebetween. For example, the magnetic moment (saturation magnetization Msxc3x97thickness t) per unit area of a first ferromagnetic layer (F1) is assumed to be larger than the magnetic moment per unit area of a second ferromagnetic layer (F2). An external magnetic field is assumed to be applied rightward in the drawing.
A resultant magnetic moment per unit area determined by the vector sum of the magnetic moment per unit area of the first ferromagnetic layer and the magnetic moment per unit area of the second ferromagnetic material layer (|Msxc2x7t(F1)+Msxc2x7t(F2)|) remains constant up to a certain point, even if the external magnetic field is increased. In an external magnetic field region A in which the resultant magnetic moment per unit area remains constant, since antiparallel coupling between the first ferromagnetic layer and the second ferromagnetic layer is stronger than the external magnetic field, the magnetizations of the first and second ferromagnetic layers are aligned in antiparallel, single-domain states.
However, the resultant magnetic moment per unit area increases as the rightward external magnetic field is further increased. Since the external magnetic field is stronger than the antiparallel coupling between the first ferromagnetic layer and the second ferromagnetic layer, the magnetizations of the first ferromagnetic layer and the second ferromagnetic layer are dispersed and the single-domain states are changed to multidomain states. Thus the resultant magnetic moment per unit area determined by the vector sum is increased. In an external magnetic field region B in which the resultant magnetic moment per unit area is increased, the antiparallel state of the ferromagnetic layers is lost. The magnitude of the external magnetic field at which the resultant magnetic moment per unit area starts to increase is referred to as a spin-flop magnetic field (Hsf).
When the rightward external magnetic field is increased further, the magnetizations of the first ferromagnetic layer and the second ferromagnetic layer are aligned in single-domain states again, and both layers are magnetized rightward this time. In this case, the resultant magnetic moment per unit area in this external magnetic field region C remains constant. The magnitude of the external magnetic field at which the resultant magnetic moment per unit area becomes constant is referred to as a saturation magnetic field (Hs).
It has been found that, when the CoFeNi alloy is used for the first ferromagnetic layer and the second ferromagnetic layer, the magnetic field at which the antiparallel state is lost, i.e., the spin-flop magnetic field (Hsf), can be satisfactorily increased compared to the case in which the NiFe alloy is used.
Experiments were conducted to determine the magnitude of the spin-flop magnetic field wherein both the first and second ferromagnetic layers comprise either a NiFe alloy (Comparative Example) or a CoFeNi alloy (Example) in accordance with the present invention.
The film structure used was substrate/nonmagnetic material layer (Cu)/first ferromagnetic layer (2.4 nm)/nonmagnetic interlayer (Ru)/second ferromagnetic layer, (1.4 nm).
When using a NiFe alloy with a Ni content of 80 atomic percent and a Fe content of 20 atomic percent in both the first second ferromagnetic layers (Comparative Example), the spin-flop magnetic field (Hsf) was approximately 59 kA/m.
By comparison, use of a CoFeNi alloy with a Co content of 87 atomic percent, an Fe content of 11 atomic percent, and an Ni content of 2 atomic percent resulted in a spin-flop magnetic field (Hsf) of approximately 293 kA/m.
As evidenced by the above experiment, the spin-flop magnetic field can be greatly improved by using a CoFeNi alloy for the first and second ferromagnetic layers as compared to the use of a NiFe alloy therein.
That is, by using a CoFeNi alloy for at least one of the ferromagnetic layer and the free magnetic layer, preferably for both layers, the spin-flop magnetic field of the ferromagnetic layer and the free magnetic layer can be effectively improved.
Next, the compositional ratio of the CoFeNi alloy will be described. The magnetostriction of a layer composed of the CoFeNi alloy is known to be shifted positively by approximately 1xc3x976xe2x88x926 to 6xc3x9710xe2x88x926 when contacted with a nonmagnetic Interlayer composed of Ru as compared to the case in which a NiFe alloy is used.
The magnetostriction is preferably in the range of xe2x88x923xc3x9710xe2x88x926 to 3xc3x9710xe2x88x926. The coercive force is preferably 790 A/m or less. If the magnetostriction is large, stress tends to increase due to film deposition strain and differences in thermal expansion coefficients among layers. By maintaining a low coercive force, the magnetization of the free magnetic layer can be satisfactorily reversed in response to an external magnetic field.
In the present invention, when a film structure of nonmagnetic material layer/free magnetic layer/nonmagnetic layer/ferromagnetic layer is employed in conduction with a CoFeNi alloy, preferably, the Fe content is in the range of 9 to 17 atomic percent, the Ni content is in the range of 0.5 to 10 atomic percent, and the balance is Co. If the Fe content is larger than 17 atomic percent, the magnetostriction is negatively increased from xe2x88x923xc3x9710xe2x88x926 and soft magnetic properties are degraded.
If the Fe content is less than 9 atomic percent, the magnetostriction exceeds 3xc3x9710xe2x88x926 and soft magnetic properties are degraded.
If the Ni content is larger than 10 atomic percent, the magnetostriction exceeds 3xc3x9710xe2x88x926 and a change in resistance (xcex94R) and a rate of change in resistance (xcex94R/R) are reduced. This is due, in part, to diffusion of Ni at the interface with the nonmagnetic layer.
If the Ni content is less than 0.5 atomic percent, the magnetostriction negatively increases from xe2x88x923xc3x9710xe2x88x926.
The coercive force can be set at 790 A/m or less if the compositional ranges described above are satisfied.
Next, when an interlayer composed of a CoFe alloy or Co is formed between the free magnetic layer and the nonmagnetic material layer, as exemplified by a film structure of nonmagnetic material layer/interlayer (CoFe alloy)/free magnetic layer/nonmagnetic layer/ferromagnetic layer, with respect to the CoFeNi alloy, preferably, the Fe content is in the range of 7 to 15 atomic percent, the Ni content is in the range of 5 to 15 atomic percent, and the balance is Co. If the Fe content is larger than 15 atomic percent, the magnetostriction is increased negatively from 3xc3x9710xe2x88x926 and soft magnetic properties are degraded.
If the Fe content is less than 7 atomic percent, the magnetostriction exceeds 3xc3x9710xe2x88x926 and soft magnetic properties are degraded.
If the Ni content is larger than 15 atomic percent, the magnetostriction exceeds 3xc3x9710xe2x88x926.
If the Ni content is less than 5 atomic percent, the magnetostriction is negatively increased from xe2x88x923xc3x9710xe2x88x926.
If the compositional ranges described above are satisfied, the coercive force can be set at 790 A/m or less.
Additionally, since the interlayer composed of the CoFe alloy or Co has negative magnetostriction, when using the CoFeNi alloy, the Fe content should be slightly decreased and the Ni content should be slightly increased as compared to when the interlayer is not interposed between the free magnetic layer and the nonmagnetic material layer.
By disposing an interlayer composed of a CoFe alloy or Co between the nonmagnetic material layer and the free magnetic layer as described above, diffusion of metallic elements between the free magnetic layer and the nonmagnetic material layer can be more effectively avoided.
In the present invention, the first antiferromagnetic layer and/or the second antiferromagnetic layers may be composed of the same antiferromagnetic material having the same composition. Consequently, the magnetization of the first ferromagnetic layer can be easily directed perpendicular to the magnetization direction of the second ferromagnetic layer, and it is possible to direct the magnetizations of the free magnetic layer and the pinned magnetic layer perpendicular to each other in the absence of an external magnetic field.
In the magnetic sensing element of the present invention, preferably, the first antiferromagnetic layer and/or the second antiferromagnetic layers are composed of any one of a PtMn alloy; an Xxe2x80x94Mn alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe; and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, wherein Xxe2x80x2 is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.
In the PtMn alloy or the Xxe2x80x94Mn alloy, the Pt content or the X content is preferably in the range of 37 to 63 atomic percent.
In the Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, the Xxe2x80x2+Pt content is preferably in the range of 37 to 63 atomic percent. Furthermore, in the Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, the Xxe2x80x2 content is preferably in the range of 0.2 to 10 atomic percent. However, when Xxe2x80x2 is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, the Xxe2x80x2 content is preferably in the range of 0.2 to 40 atomic percent.
By using the alloys in the appropriate compositional ranges described above, followed by annealing, a first antiferromagnetic layer and second antiferromagnetic layers generating large exchange coupling magnetic fields can be obtained. In particular, by using PtMn alloys, it is possible to obtain a first antiferromagnetic layer and second antiferromagnetic layers which generate exchange coupling magnetic fields of 48 kA/m or more, for example, exceeding 64 kA/m, and which have a significantly high blocking temperature of 380xc2x0 C., the blocking temperature being a temperature at which the exchange coupling magnetic fields are lost.
Although these alloys have a disordered face-centered cubic (fcc) structure immediately after being deposited, the structure is transformed into a CuAuI-type ordered face-centered tetragonal (fct) structure by annealing.
The present invention further provides a magnetic sensing element comprising a multilayer film core structure, wherein the core structure includes an underlayer; a antiferromagnetic layer; a synthetic ferri-pinned-type pinned magnetic layer comprising a first pinned magnetic sublayer, a nonmagnetic intermediate sublayer, and a second pinned magnetic sublayer; a free magnetic layer comprising a diffusion-preventing layer and a magnetic layer; and a nonmagnetic layer.
In accordance with the present invention, a method for making a magnetic sensing element includes the steps of:
(a) forming a multilayer film on a substrate, the multilayer film including a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, a free magnetic layer, and a nonmagnetic layer;
(b) annealing the multilayer film at a first annealing temperature in a first magnetic field having a first magnitude so as to pin the magnetization of the pinned magnetic layer in a predetermined direction;
(c) forming a first resist layer for a lift-off process on the nonmagnetic layer, the lower surface of the first resist layer having cutout sections;
(d) forming ferromagnetic layers on the nonmagnetic layer;
(e) forming second antiferromagnetic layers on the ferromagnetic layers; and
(f) annealing the multilayer film at a second annealing temperature in a second magnetic field having a second magnitude so as to pin the magnetization of the free magnetic layer in a direction substantially perpendicular to the magnetization direction of the pinned magnetic layer.
In the present invention, the multilayer film formed in step (a), in which the nonmagnetic layer is the uppermost layer, is annealed in the first magnetic field, and in step (e), a ferromagnetic material and an antiferromagnetic material are deposited on the nonmagnetic layer. Consequently, it is possible to obtain a magnetic sensing element in which the ferromagnetic layers and the second antiferromagnetic layers are formed on the planar upper surface of the nonmagnetic layer.
In the present invention, since the multilayer film is annealed in the magnetic field to pin the magnetization of the pinned magnetic layer in the predetermined direction in the state in which the second antiferromagnetic layers are not formed on the multilayer film, when the second antiferromagnetic layers are formed on the multilayer film, exchange anisotropic magnetic fields are not generated between the second antiferromagnetic layers and the ferromagnetic layers.
That is, the exchange anisotropic magnetic fields by the second antiferromagnetic layers are generated for the first time in step (f) so as to change the magnetization direction of the free magnetic layer easily to the predetermined direction. Therefore, the magnetization direction of the free magnetic layer is easily pinned in the direction substantially perpendicular to the magnetization direction of the pinned magnetic layer.
In step (f), the second annealing temperature is preferably lower than the blocking temperature of the first antiferromagnetic layer, and the magnitude of the second magnetic field is preferably smaller than the exchange anisotropic magnetic field of the first antiferromagnetic layer.
In the present invention, in steps (d) and (e), the ferromagnetic layers, the second antiferromagnetic layers, and electrode layers are continuously deposited using the first resist layer as a mask, and the first resist layer is then removed. Thereby, in the resultant magnetic sensing element, the electrode layers are placed on the second antiferromagnetic layers, and the edges of the electrode layers at the track width region sides overlap with the edges of the second antiferromagnetic layers at the track width region sides.
After step (e), the method for making the magnetic sensing element may further include the steps of:
(g) removing the first resist layer;
(h) forming a second resist layer for a lift-off process on the nonmagnetic layer and the second antiferromagnetic layers, the second resist layer having cutout sections;
(i) forming electrode layers on the second antiferromagnetic layers; and
(j) removing the second resist layer.
Consequently, in the resultant magnetic sensing element, the electrode layers are formed on the second antiferromagnetic layers, and the edges of the electrode layers at the track width region sides are placed closer to the side faces of the multilayer film compared to the edges of the second antiferromagnetic layers at the track width region sides.
Alternatively, after step (e), the method may further include the steps of:
(k) removing the first resist layer;
(l) forming a second resist layer for a lift-off process on the nonmagnetic layer, the second resist layer having cutout sections, the width in the track width direction of the bottom face of the second resist layer being smaller than the width of the bottom face of the first resist layer;
(m) forming electrode layers on the nonmagnetic layer and the second antiferromagnetic layers; and
(n) removing the second resist layer.
Consequently, in the resultant magnetic sensing element, the electrode layers are placed on the second antiferromagnetic layers, the edges of the electrode layers at the track width region sides extend from the edges of the second antiferromagnetic layers at the track width region sides toward the central region of the multilayer film.
When a CPP-type magnetic sensing element is fabricated, preferably, the method further includes: before step (a), step (o) of forming a lower electrode layer on the substrate; and after step (e), step (p) of masking the central region in the track width direction of the nonmagnetic layer; step (q) of forming an insulating layer on the second antiferromagnetic layers; and step (r) of forming an upper electrode layer electrically connecting to the multilayer film.
More preferably, the method further includes: between step (o) and step (a), step (s) of forming a protruding section which protrudes toward the multilayer film in the center in the track width direction of the lower electrode layer; and step (t) of forming insulating layers on the side regions in the track width direction of the lower electrode layer; and in step (a), the multilayer film is formed so that the upper surface of the protruding section is in contact with the lower surface of the multilayer film.
In step (t), preferably, the upper surface of the protruding section is flush with the upper surfaces of the insulating layers provided on the side regions of the lower electrode layers.
Preferably, the lower electrode layer and/or the upper electrode layer are composed of a magnetic material. Consequently, the lower electrode layer and/or the upper electrode layer function as the lower shielding layer and/or the upper shielding layer.
The upper electrode layer may be a laminate including a nonmagnetic conductive layer electrically connected to the multilayer film and a magnetic layer.
In the present invention, preferably, the nonmagnetic material layer is composed of a nonmagnetic conductive material. The magnetic sensing element in which the nonmagnetic material layer is composed of a nonmagnetic conductive material is referred to as a spin-valve GMR-type magnetoresistive element (CPP-GMR).
In the CPP-type magnetic sensing element of the present invention, the nonmagnetic material layer may be composed of an insulating material. Such a magnetic sensing element is referred to as a spin-valve tunneling magnetoresistive element (CPP-TMR).
Additionally, if the nonmagnetic layer is composed of one of Ru, Rh, Ir, Os, and Re, or an alloy of at least two of these elements in step (a), the surface of the nonmagnetic layer is not substantially oxidized in step (b). Therefore, even if the surface of the nonmagnetic layer is not treated by milling or the like before the ferromagnetic layers are formed by sputtering in step (d), RKKY interactions can be generated by the free magnetic layer and the ferromagnetic layers with the nonmagnetic layer therebetween.
That is, in accordance with the method for making the magnetic sensing element of the present invention, since the interfaces between the nonmagnetic layer and the ferromagnetic layers are not required to be trimmed by milling, it is possible to prevent a decrease in the unidirectional anisotropic magnetic field for aligning the magnetization direction of the free magnetic layer in each side region in a predetermined direction.
However, since the free magnetic layer and the ferromagnetic layers are magnetically coupled to each other with the nonmagnetic layer therebetween by the RKKY interactions, even when the interfaces between the nonmagnetic later and the ferromagnetic layers are surfaces trimmed by milling, it is possible to obtain unidirectional anisotropic magnetic fields having a magnitude sufficient for aligning the magnetization directions in the side regions of the free magnetic layer in a predetermined direction.
In step (a), preferably, the nonmagnetic layer is composed of Ru and the thickness of the nonmagnetic layer is set at 0.8 to 1.1 nm.
Alternatively, in step (a), preferably, a conductive material layer placed between the nonmagnetic layer and the free magnetic layer, the conductive material layer having a lower resistivity than that of the nonmagnetic layer. In such a case, more preferably, the nonmagnetic layer is composed of Ru and has a thickness of 0.4 to 1.1 nm, and the conductive material layer is composed of Cu and has a thickness of 0.3 to 0.5 nm.
Preferably, in step (a), the pinned magnetic layer is formed by laminating a plurality of ferromagnetic layers having different magnetic moments (Msxc3x97t) per unit area, a nonmagnetic interlayer being placed between the two adjacent ferromagnetic layers.
Preferably, in step (a), the free magnetic layer is formed by laminating a plurality of ferromagnetic layers having different magnetic moments (Msxc3x97t) per unit area, a nonmagnetic interlayer being placed between the two adjacent ferromagnetic layers.
Preferably, the nonmagnetic interlayer is composed of any one of Ru, Rh, Ir, Os, Cr, Re, and Cu, or an alloy of at least two of these elements.
In the present invention, the same antiferromagnetic material may be used for the first antiferromagnetic layer and the second antiferromagnetic layers.
Preferably, the first antiferromagnetic layer and/or the second antiferromagnetic layers are composed of any one of a PtMn alloy, an Xxe2x80x94Mn alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, wherein Xxe2x80x2 is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.